Electrolytic cell



Feb. 13, 1940.

c. c. GAUT ET AL ,286

ELEGTROLYTI C CELL Filed Feb. 28, 1938 Jim alum i'hdent/f [lag m5 INVE ORS ATTORNEY Patented Feb. 13, 1940 UNITED STATES PATENT OFFICE ELECTROLYTIC CELL Application February 28, 1938, Serial No. 193,192 In Great Britain October 19, 1937 4 Claims.

This invention concerns dry electrolytic con-- densers and like electrolytic cells.

An object is to provide an improved conductive spacer for use between the electrodes of such 5 a device.

Other objects of the invention will be apparent from the following description taken in connection with the appended claims.

The present invention comprises the combination of elements, methods of manufacture, and the product thereof brought out and exemplified in the disclosure hereinafter set forth, the scope of the invention being indicated in the appended claims.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the meth- 0d of procedure and the combination of elements without departing from the spirit of the inveni0 tion.

In the drawing:

Figure 1 illustrates a step in making the spacers of the present invention;

Figure 2 illustrates a condenser assembly em- 5 bodying the spacers of the invention; and

Figure 3 shows a completed condenser.

According to the invention this object 7 is achieved by immersing a paper sheet, strip or the like in a liquid mixture formed by adding 0 together a solution of a suitable cellulose derivative, at least-one ionogen, and at least one highboiling liquid which is not a solvent for the cellulose derivative and then drying this composition. "The term immersing is to be taken to 5 include both actual immersion of the paper in the liquid mixture, e. g. by passage of the paper through a bath, and deposition of the liquid mixture on to the paper. The amount of liquid mixture used is sufiicient to allow liquid electroo lyte to exude from the deposited fllm into the paper as the solvent for the cellulose derivative evaporates. Thus paper of .002" thickness may be provided with suflicient of the mixture to give a final thickness of from .003 to .005".-

5 The paper used should be an absorbent paper with an open structure and should be of good purity. The thickness mentioned for the paper can be varied; thus a thinner paper may be used if care is taken to avoid damage in handling and D in anyevent the thickness should not be so great as to prevent thorough saturation of the paper by the exuded electrolyte.

The conductive spacer prepared in this way is used without subsequent impregnation, thus avoiding the necessity for the usual impregnating paste and the usual impregnating operations. Due to the absence of impregnation the product is one which requires none of the usual cleansing operations following upon impregnation, particularly at the terminal tags, and the spacer is 5 quickly made, easy to handle, and safe from the point of view of electrolyte seeping out of the cell and causing corrosion.

The spacer may be used immediately after manufacture if desired or stored for future use; 10 it is readily reeled when in strip form.

The term suitable cellulose derivative is to be understood to exclude derivatives which produce corrosion of the electrodes upon decomposition, such as nitrocellulose, and those which 1 contain free sulphates or chlorides. The preferred derivative is cellulose acetate but ethyl cellulose and cellulose aceto-butyrate may be mentioned as suitable alternatives. The solvent is preferably a low-boiling solvent such as acetone, methyl acetate or ethyl formate but a solvent of higher boiling point than these, such as ethylene glycol diacetate, may be used provided that it is one that evaporates more quickly from the mixture during casting than the high-boiling liquid; two or more of these solvents may, of course, be used simultaneously. In some cases the solvent, which is given off from the treated paper, may be recovered.

The ionogen may be one or more of the acids used in the formation of conductive compositions for electrolytic condensers, such as citric or boric acid, and/or one or more stable salts thereof, preferably ammonium salts.

Ethylene glycol, diethylene glycol, triethylene 85 glycol and glycerine are suitable high-boiling liquids.

If desired the mixture may also include an organic borate compound such as amyl borate and/or a filler such as shellac or colophony resin. 40

It is preferable that the ionogen and the highboiling liquid should be partially or wholly combined to give a reaction product since this increases the stability of the conductive mixture.

Ingredients 3 and 4 are mixed together and heated at 135 C. and ingredients 5, 6 and '7 are also mixed together, the latter mixture being ingredient 2. The final mixture is diluted with 6 litres of acetone, and is then preferably filtered and -de-aerated, e. g. by heating or suction. In the mixing operations use should be made of stirring means which cause no reaction in the mixture and do not dissolve, e. g. of glass,

. aluminum or stainless steel.

The paper treated with the product thus obtained is fed onto the surface of a casting band or drum and maintained at an elevated tempera-' ture, e. g. 30" C. or more, the acetone being thus removed and, if desired, recovered. The speed of the paper is comparatively critical and in this Example should not depart appreciably from the value of 1.75 ft./min. The casting surface should be of aluminum, stainless steel, or other material having no detrimental effects on the mixture.

Example II.--Ingredient 4 of Example I is replaced by the same quantity of ammonium borate. In all other respects the manufacture is the same as that specified in Example 1.

Referring to the drawing Figure lshows paper strip l0 being led through the mixture II, which is one of the mixtures heretofore described, so as to coat and saturate the paper with the mixture, the coating l2 being shown exaggerated in the drawing. The treated paper is then fed onto the surface of casting drum l3 where the solvent is evaporated.

Figure 2 shows a condenser assembly comprising treated paper spacers ll! of the present invention assembled with electrodes l4 and I5 of 40 film forming metal, atleast one of which is filminto a roll it and enclosed in a-container l9 provided with an insulating disc top 20 having terminals 2i and 22 connected respectively to tabs l6 and I1.

While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby but it is intended to cover the invention broadly within the spirit and scope of the appended claims.

What is claimed is:

1. A film-maintaining spacer for dry electrolytic condensers comprising a paper base, a porous, non-tacky cellulose derivative selected from the 'group consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate embodied therein and thereon, and an ionogen-and a high boiling liquid intimately embodied in the cellulose derivative, said ionogen being at leastone of the materials selected from the group consisting of acids used in the formation of conductive compositions for electrolytic condensers and the stable salts thereof, and said high boiling liquid being selected from the group consisting of glycerine and the glycols. I

2. A spacer for dry electrolytic condensers comprising a paper base, a cellulose derivative selected from the group consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate embodied therein and thereon, and an electroylte comprising an ionogen and a high boiling liquid embodied in the cellulose derivative, said cellulose derivative comprising a non-rtacky, nonhomogeneous, porous matrix carrying said electrolyte, said spacer being capable of maintaining a current-blocking film on acondenser electrode during operation of the condenser with said spacer interposed between the electrodes thereof.

3. The method of making a non-tacky, nonhomogeneous, porous conductive. film-maintaining spacer for dry electrolytic condensers which comprises dissolving a cellulose lderivative selected from the group consisting of cellulose acetate, ethyl cellulose and cellulose aceto-butyrate, at least one ionogen and at least one high boiling liquid which is not a solvent for the cellulose derivative in a volatile solvent, immersing a strip of paper in the mixture thus produced and evaporating the volatile solvent from the treated paper.

4. The method of making a non-tacky, nonhomogeneous, porous conductive film-maintaining spacer for dry electrolytic condensers which comprises dissolving the following ingredients in a common volatile solvent: (1) a cellulose derivative selected-from the group consisting of cellulose acetate, ethyl cellulose and cellulose acetobutyrate, (2) at least one ionogen selected from the group consisting of acids used in the formation of conductive compositions for electrolytic condensers and the stable salts thereof and (3) at least one high boiling liquid selected from the group consisting of glycerine and the glycols,

immersing a strip of paper in the mixture thus produced and then evaporating the volatile 501-.

vent from the treated paper. 

